Cluster structure of 16 O, 18 O and 20 O is investigated by the antisymmettrized molecular dynamics (AMD) plus generator coordinate method (GCM). We have found the K π =0 + 2 and 0 − 1 rotational bands of 18 O that have the prominent 14 C+α cluster structure. Clustering systematics becomes richer in 20 O. We suggest the K π =0 + 2 band that is the mixture of the 12 C+α+4n and 14 C+ 6 He cluster structures, and the K π =0 − 1 band that has the 14 C+ 6 He cluster structure. The K π =0 + 3 and 0 − 2 bands that have the prominent 16 C+α cluster structure are also found.
⌬-isobar excitation in the nuclear medium yields an effective three-nucleon force. A coupled-channel formulation of nucleon-deuteron scattering with ⌬-isobar excitation developed previously is used. The threeparticle scattering equations are solved by a separable expansion of the two-baryon transition matrix below the inelastic threshold of pion production. The effect of ⌬-isobar excitation on the spin-averaged differential cross section is studied. The discrepancy between theory and experiment in the diffraction minimum is reduced. ͓S0556-2813͑98͒06510-8͔
The importance of including experimental resonances in constructing effective inter-cluster interactions has been investigated. For this, we first address the question of how to obtain the analytical properties of the Jost function in regions of physical interest on the complex kplane when the potential is given in a tabular form. We then employ the Marchenko inverse scattering method to construct, numerically, phase equivalent local potentials supporting the same bound state(s) but having different resonance spectra which affect the off-shell characteristics of the corresponding scattering amplitudes. This implies that the inclusion of the experimental resonances in constructing a potential would change its shape, strength, and range which in turn would modify the bound and scattering wave functions in the interior region. This is expected to have important consequences in calculations of transition amplitudes in nuclear reaction theories, which * Nuclear Physics A in press † Permanent address:
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